Browsing by Subject "Large eddy simulation (LES)"

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    A Comparison of 1-Way and 2-Way Nesting in the WRF-LES Framework
    (2013-05) Hawbecker, Patrick; Kang, Song-Lak; Bruning, Eric; Hopson, Thomas; Kosovic, Branko
    The Weather Research and Forecasting (WRF) model is a numerical model designed for numerical weather prediction of the Earth’s atmosphere. Although it is commonly used for mesoscale modeling, it is capable of running Large Eddy Simulations, or LES. LES is an approach to directly solve turbulent eddies within the atmospheric boundary layer by filtering the Navier-Stokes equations and directly resolving the large, turbulent eddy fields. This is most useful for boundary layer applications, which is the region of the atmosphere in which we spend the majority of our lives. LES typically works with a smaller domain due to having a much smaller grid size than mesoscale models and can be used for applications such as simulating flow over topography, flow through wind farms, and convective initiation in thunderstorms. One useful feature in numerical models is placing a higher resolution domain within a coarser, parent domain. This feature is called nesting and is useful for more accurately resolving the areas of interest, while still resolving the surrounding environment that may affect the area of interest. Nesting can be done in two ways: 1-way nesting, and 2-way nesting. The two nesting techniques are very similar, but can produce extremely different results. Here, the two techniques are compared in a variety of ways to determine the usefulness, accuracy, and any unwanted issues that may result from using nests in a numerical simulation.
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    Atmospheric boundary layer evening transitions over West Texas
    (Texas Tech University, 2008-12) Ruiz-Columbie, Arquimedes
    In the circadian Atmospheric Boundary Layer (ABL) cycle over land, transitions occur between two fundamental modes through near-neutral conditions. Such diurnal cycles show two major stages: first, the unstable mode and its mixed layer take place after sunrise and persist until the late afternoon or the evening when a transition happens. Second, the stable mode and its stable layer form after sunset and begin to dissipate the following morning giving room to a transition after which the mixed layer will occur again. The transition periods are not fully understood, but surely important. In particular, the features of the evening transition (ET) period may influence the inception and strength of the nocturnal low level jet (LLJ) and the whole structure of the nocturnal atmospheric boundary layer (NABL). If moisture sources are available, they also might determine whether the nocturnal surface is going to be characterized by condensation (weak LLJ and shallow NABL) or by continued evaporation (windy deep NABL). In this dissertation, three data subsets (radiation, meteorology, scintillometry) proved very useful in the characterization of the ET; within each of these subsets, particular selected quantities allowed the precise determination of ET timelines. Numerical modeling also played an important role in understanding and characterizing the ET.